I am looking for advice on how to wire my new humidistat with my furance and humidifier. First, here are the components I'm working with:
- Furnace: Carrier WeatherMaker Infinity (Model 58MVP100 14120)
- Humidifier: Honeywell HE265B1005
- Humidistat: HoneywellH6062
Background: Old humidistat (Honeywell H1008A) quit working so ordered this new one. The humidifier is a Bypass, with both humidistat and humidifier mounted on the Return side. Humidifier is hooked into COLD water line.
What I'd Like: Since humidifier is on Return side and hooked into cold, I'd want the humidifier to kick on when humidity reads low and there is a call for heat. (Feel free to let me know if you feel differently).
Where I am at in the setup: I do have the humidistat hooked up to constant 24V and the Outdoor Sensor hooked up and tested.
What I need help with:
My furnace does have a 24V HUM terminal which kicks on during call for heat, so I know I can use that, I just need to know how to hook it in. On my humidistat I have two U terminals for the humidifier, and I need to know how to hook those up to the furnace and humidifier solenoid. I will post some pictures. I know the bottom U humidistat terminal gets wired to one of the humidifier solenoid wires. The top U terminal is what I need help with….and then I need help with what wire to hook into the second humidifier solenoid wire. One note, my furnace does have the HUM 24V terminal, as well as a HUMR (HUM relay) terminal. 
Best Answer
It goes "HUM -> U, other U->solenoid terminal, other solenoid terminal->C"
In order to get your humidifier to work, you need to create a closed circuit through the humidifier solenoid to bring 24VAC to it. Since we know the HUM 24V terminal is a 24VAC source from the wiring diagram you posted with the C terminal as its corresponding return, we can pull 24VAC from that and feed it to one U terminal on the humidistat. The other U terminal, then, connects down to one of the humidifier's solenoid connections; finally, the remaining terminal on the humidifier solenoid gets connected to the C wire on your furnace. The result is a closed circuit that only is energized when your furnace permits humidification and the humidistat calls for water, just as you wish it to work.